The phosphor is utilized in a fluorescent display tube (VFD: vacuum fluorescent display), a field emission display (FED), a plasma display panel (PDP), a cathode-ray tube (CRT) a white light-emitting diode (LED), and so on. In any of these applications, it is necessary to provide the phosphor with energy to excite the phosphor in order to have the phosphor emit the fluorescent light and the phosphor is excited by an excitation source with high energy such as a vacuum ultraviolet ray, an ultraviolet ray, an electron beam, and a blue light so as to emit a visible light ray. However, as a result that the phosphor is exposed to such excitation source, the brightness of the phosphor is lowered so that the phosphor itself tends to be degraded. Therefore, the phosphor having the brightness little degraded is desired. Therefore, a sialon phosphor has been proposed as a phosphor having the brightness little degraded instead for the conventional phosphor such as silicate phosphor, phosphate phosphor, aluminate phosphor, and sulfide phosphor.
As an example of these sialon phosphors is manufactured in the following manufacturing process as generally described below. First, silicon nitride (Si3N4), aluminum nitride (AlN), Europium oxide (Eu2O3) are mixed at predetermined molar ratios thereof and the resultant mixture is fired by a hot press method in one atmosphere (0.1 MPa) of nitrogen atmosphere at 1700 degree Celsius for one hour (for example, refer to Patent reference 1). It was reported that α-sialon activated by Eu ion manufactured in the above process became a phosphor to emit a yellow light of wavelength region of 550 nm to 600 nm if it is excited by the blue light having a wavelength region of 450 to 500 nm.
Further, a blue phosphor activated by Ce having a host crystal of JEM phase (LaAl(Si6-zAlz)N10-zOz) (refer to Patent reference 2), a blue phosphor activated by Ce having a host crystal of La3Si8N11O4 (refer to Patent reference 3), and a red phosphor activated by Eu having a host crystal of CaAlSiN3 (refer to Patent reference 4) are known.
However, a phosphor which emits a green luminescence as well as phosphors which emit a blue luminescence and a yellow luminescence, respectively, is in demand for the application to a plasma display and a white light LED utilizing an ultraviolet LED as an excitation source.
[Patent reference 1] Japanese patent application publication No. 2002-363554.
[Patent reference 2] Japanese patent application No. 2003-208409.
[Patent reference 3] Japanese patent application No. 2003-346013.
[Patent reference 4] Japanese patent application No. 2003-394855.
As another sialon phosphor, a phosphor of β-sialon doped with a rare earth element is also known (refer to Patent reference 5) and it is shown that phosphors activated by Tb, Yb, and Ag are those which emit a green light of 525 nm to 545 nm. However, a phosphor having a high brightness has not been obtained since the activating elements do not solid solve adequately into the host crystal, but reside in the boundary phase because the synthesis temperature is so low as 1500 degree Celsius.
[Patent reference 5] Japanese patent application publication No. S60-206889.
As another sialon phosphor, a phosphor of β-sialon doped with divalent europium is also known (refer to Patent reference 6) and it is shown that the phosphor becomes a green phosphor. However, the emission intensity of the green light is particularly so strong that the phosphor would become more desirable as a sialon phosphor.
[Patent reference 6] Japanese patent application No. 2004-070894.